Rasmussen, Gallup at odds over Obama's approval

Rasmussen and Gallup's tracking polls have been mutually reinforcing this year. Neither strays much from the other, and each has suggested a Margin of Error Race that's far closer to reality than, for example, Bloomberg's weird poll last week showing the president up by 13%.

But there's a decided veer in the most recent results on Sunday.

Gallup has Barack Obama's net approval rating at +6%, while Rasmussen has it at -10%. That's a pretty astounding 16% gap.

That disparity carries over to their presidential preference polls, too. Gallup has Obama up 46%-45%, while Rasmussen has Romney in front, 48%-43%. That's a 6% gap.

So what's going on?

One possibility is that Gallup uses a seven day rolling average, while Rasmussen only uses a three day roll, but is that really enough to explain a 16% gap on job approval?